Fill & Bleed Applications

A Fill and Bleed Circuit
is combination of pneumatic valve components used to inflate a volume or apparatus in one controllable function and to release or vent pressure in a second controllable function.

Fill and Bleed Circuits are commonly used in many applications where a particular pressure, firmness or position can be controlled with the addition or venting of pressure.

Pressure control systems typically use a fill and bleed type circuit to add or subtract air in maintaining pressure. They can also be referred to as E/P or Electronic Pressure Control when feedback is provided to read the downstream or output pressure and looped back to tell a PLC or System to fill or bleed more pressure. These can be tremendously accurate depending on the speed and orifice of the valves used in the circuit and the accuracy of a pressure transducer.

Clippard EV valves are commonly used in these applications in analytical and instrumentation equipment, medical devices such as blood pressure cuffs, and pressure control industrial applications.

In lumbar support applications, pressure would be better defined as firmness, where a pneumatic fill and bleed circuit is controlling the air pressure in a flexible bladder built into a seat. Massage or therapy chairs use multiple bladders filling and bleeding pressure that changes the firmness in a sequential pattern massaging the user. These applications can be found in first-class airline seats, train seats, truck or mobile cabs where the operator is sitting for extended periods of time.

Position is based on the same principle when applying a fill and bleed circuit along with the basic cylinder formula of  ^{PRESSURE X AREA = FORCE}  and linear spring force. Using s single acting cylinder, the linear spring force on the cylinder needs to be overcome with a particular pressure in order to move. As the cylinder moves, the force required to push against the spring force changes, therefore varying the pressure can simply vary the position. For example, if a cylinder was used to move the position of a table up or down, a fill and bleed circuit can be applied to the bottom of the cylinder to adjust pressure, which in turn changes the position.

The components can be quite simple and robust, such as the FBV manual fill and bleed valves. Or, for integration with electronic controls, a combination of electronics valves can achieve very simple or more complex circuit for your fill and bleed applications.

Clippard has made hundreds of different fill and bleed circuits for many different application and industries. Contact us today for assistance with circuit design, sub-assemblies quotes, or just to chat.

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